Bistable actuator device

Abstract: An actuator device is described, apt at varying its functional condition from a state of rest to a working state, both stable, comprising a body (2,3) of contained dimensions, within which the following are housed: actuating means, comprising a thermal actuator (5), an electric heater (6), electric contacting elements (7) and a transmission shaft (10,11) of the thrust generated by the actuator (5); means for maintaining the working state, also in absence of electrical supply to the actuating means, comprising bistable kinematic motion (20-30) of inclined planes and/or cams.

Description: The present invention relates to a bistable actuator device, i.e. an actuator device apt at assuming two states, both of which being stable, and in which the commutation between the two different states is commanded by an external intervention. In other words, a bistable actuator device is apt, during its first functional cycle, to reach a determined working condition and to maintain it, to then return to the previous working condition, in following a successive functional cycle; such actuator systems therefore have actuator means and means for maintaining the condition reached on termination of the first functional cycle; the actuator devices of the cited type contrast with those without means for maintaining the position when their supply is stopped (monostable actuator systems). Bistable actuator systems in practice are utilised for numerous applications: for example they are used for the realisation of blocking systems of the doors of electrical household appliances, so as to avoid dangerous operations for the user. Thermal bistable actuator systems are known, in which the maintaining of the position reached is assured by way of a couple of bimetallic elements; such known systems however lack appropriate functional control means, so that their way of operating, which is based on ambient temperature, easily results in being affected by external sources of heat. Electro-magnetic bistable actuator systems are also known, that however depend upon complex circuitry for controlling the polarity inversion or the electric commutation. Another typical problem of the known art is that of the complexity of the components making up the bistable devices, and their arrangement; for example the use of electromagnets makes the actuator devices complex, bulky and expensive. A further problem of known thermal or electric bistable systems is the reduced run available, together with the high forces to be used; normally, with the purpose of obtaining greater forces with devices of contained dimensions, the electric actuator means of devices in use must normally be sized for a very brief supply time; in such cases there is however the risk that accidental extended times of supply cause the destruction of the actuator device. From US-A-5,222,277 a device is known, comprising means for obtaining a bi-directional movement of a binge and allowing the latter to maintain a working position even when a relevant monostable actuator is deactivated; according to this solution, a linear trust of the actuator has to be converted into a bi-directional rotation of the hinge. The principal purpose of the invention is that of overcoming the aforementioned drawbacks and to indicate a bistable actuator device that is simple, economical and reliable in the most varied conditions of use; another purpose of the invention is that of indicating a bistable actuator that, even being of very contained dimensions, is able to originate great forces and runs, and is able to work with long or short periods of supply and/or insertion. Such purposes are reached according to the present invention by way of an actuator device having the characterizing features of the annexed claim 1. Further characteristics and advantages of the present invention shall result in being clear from the following detailed description and annexed drawings, supplied purely as an explanatory and non-limiting example, wherein; figure 1 is a partial sectioned elevation of the device according to the invention, in a first functioning condition; figure 2 is a sectioned view of the device according to the invention, carried out according to the line W-W of figure 1 ; figure 3 is a sectioned view of the device according to the invention, carried out according to the line A-A of figure 1 ; figure 4 is a sectioned view of the device according to the invention, carried out according to the line B-B of figure 2; figure 5 is a view, similar to that of figure 1, of the device according to the invention, in a second functioning condition; figure 6 is an elevation of the device according to the present invention, in an embodiment being particularly advantageous. In the mentioned figures, reference number 1 indicates the bistable actuator device as a whole according to the present invention; 2 indicates a body in which a monostable type actuator is housed; with 3 a substantially tubular shaped body is indicated within which kinematic means are housed; the diameter of the body 3 is extremely contained (approximately 17 mm). As can be seen from figure 2, a chamber 4 is defined in the body 2 which houses: a thermal actuator, or thermoactuator 5, an electric heater 6, for example a positive temperature coefficient resistor PTC, arranged in contact with the thermoactuator 5; two electric supply terminals 7, exiting the body 2. The thermoactuator 5 comprises a conductive body 8, which is thermally and electrically connected to the heater 6 supplied by two electric terminals 7. The two terminals 7, the thermoactuator 5 and the heater 6 constitute an electrical heating circuit that, due to the effect of the PTC heater, is self-regulating in its temperature. In the body 8 of the thermoactuator 5 a sealed chamber is defined, filled with a thermal expandable material 9, for instance wax; in such sealed chamber a small piston 10 is arranged, the extremity 10A of which exits the body 8 of the thermoactuator 5; the expansion of the material 9, when subjected to an increase in temperature (induced by the heater 6 electrically supplied by way of the terminals 7) induces a thrust on the piston 10, and therefore a linear movement of the same, so as that the extremity 10A is distanced from the body 8. With 11 a mobile rod is indicated, an extremity 11A of which exits the body 2; said rod 11 is subjected to the contrary reaction of an elastic element, for instance a spiral spring 12; the spring 12 is able to cause, acting upon the seat 11B, by way of the rod 11, the re-entry of the piston 10 in the thermoactuator 5 upon termination of the heating cycle of the latter. The thermoactuator 5, the heater 6, the electrical contacts 7, the rod 11, the spring 12 and the body 2 constitute as a whole a thermoelectric monostable actuator device DA, i.e. capable of thrust operating only when electrically supplied, but not able to maintain the position reached once supply is withdrawn. The body 2 of the thermoelectric actuator device is mechanically coupled to the body 3; in particular with 13 and 14 two flanges are indicated making up part respectively of the bodies 2 and 3, equipped with a bayonet type hooking system for their mutual joining; with 15 and 16 coaxial holes are indicated being present in said flanges, useful for the fixing of the device 1 to another device; the distance between the hooks 15-16 visible in the upper and lower part of the figure is approximately 26 mm. The body 3 is internally equipped with a bistable kinematic motion, i.e. apt at consenting the maintenance of the working position reached, determined by the activation of the thermoactuator 5, even upon termination of the supply to the latter. The body 3 and the said internal kinematic motion therefore constitute a bistable adapter CB, apt at transforming the monostable actuator DA in the bistable actuator device 1. The bistable kinematic motion comprises a sliding cursor element 20 linearly slidable within the body 3, and restrained in its movement by a pair of appropriate guides 21A and 21B obtained as protrusions on the internal wall of the body 3; with 22 a mobile element is indicated, also being linearly slidable within the body 3 and capable of being made to rotate by the thrust of the sliding cursor 20, with 23 an elastic element is indicated, such as a spiral spring, acting between the extremity of the body 3 and the rod 24, partially inserted in the mobile element 22. The guides 21A and 21B, the sliding cursor and the element 22 have a system of inclined planes and/or cams able to transform the linear movement of the piston 10, of the rod 11 and of the sliding cursor 20 in a rotary movement of the mobile element 22. The sliding cursor 20, of a circular section, has at one of its extremities a seat 20A apt at containing the extremity 11A of the rod 11; on the edge of the opposite extremity of the sliding cursor 20 small teeth 25 are obtained (figure 1), that therefore create a series of inclined planes 26; on the external surface of the sliding cursor 20 four radial protrusions or contours are also defined; as seen in figure 4, such contours indicated with 27 cooperate with the guides 21A and 21B of the body 3 for consenting only a linear movement of the sliding cursor 20; as can be seen in figure 2, the two guides 21A also have an edge provided with inclined planes, indicated with 28 and 29. The mobile element 22 has in its lower part a circular section of a diameter being less than that of the sliding cursor 20, from which four radial teeth 30 are obtained (see figure 3), of a length being less than that of the overall mobile element 22; the extremity 30A of such teeth 30 pointing towards the sliding cursor 20 is not flat, but inclined. As can be seen from figures 1, 2 and 5, the mobile element 22 is capable of being partially inserted in the sliding cursor 20; to the mobile element 22 an extremity of the said rod 24 is then introduced; its other extremity exits from the body 3. The forms and dimensions of the details 20 and 22, the guides 21A and 21B and of the body 3 are calculated so as that the sliding cursor 20 is guided, by way of the guides 21A-21B and contours 27, to slide for all its linear movement, and the mobile element is guided, by way of the guides 21A-21B and teeth 30, only for a limited section of its path. The functioning of the device subject of the present invention is described in the following; to such purposes it is to be noted that the initial condition of the device is that as illustrated in figure 5. The thermoactuator 5, when not electrically supplied by way of the terminals 7, is subject to the reaction of the spring 12, the force of which is greater than the thrust exercised on the piston 10 by the material 9, when this is not heated: in such condition the extremity 10A of the piston 10 is in a withdrawn position. When the terminals 7 are connected to a source of electrical supply, the heater 6 (PTC) heats, thermo-adjusting automatically its temperature; the heat thus created is transferred by contact to the body 8 of the thermoactuator 5, and therefore to the expandable material 9 contained within the sealed chamber. The increase of temperature of the thermoactuator 5 determines an increase in volume of the expandable material 9 and therefore a thrust on the piston 10; it is to be noted that the temperature and the relation between the volume of the sealed chamber and the volume of the expandable material 9 is appropriately calculated, so as to allow a precise increase in pressure and to enable movement of the piston 10 and the rod 11 without exceeding in thrust. The extremity 10A of the piston 10 pushes the rod 11, which in turn operates a thrust on the sliding cursor 20; such sliding element 20 therefore linearly slides in the guides 21A and 21B, integral with the body 3, and thrusts, with its inclined planes 26, the inclined extremity 30A of the teeth 30 of the mobile element 22. The mobile element 22 also slides in a linear manner, restrained by the guides 21A-21B and contours 30, but only for a brief section (for example during the first phase of the actuation cycle), also moving linearly the rod 24 in contrast to the action of the spring 23. The resulting force on the rod 24 corresponds therefore to the difference between the force of the thermoactuator 5 and the contrary forces of the springs 12 and 23. The mobile element 22 moves in a linear manner until is not pushed by the sliding cursor 20 over the extremity of the guides 21A and 21B, or better until its teeth 30 are no longer restrained by the guides 21. Thus, in the terminal part of its run (i.e. some instants before the interruption of supply to the thermoactuator) the mobile element 22 is no longer restrained by the guides 21A and 21B: at this point, the thrust between the inclined planes 26 of the sliding cursor 20 and the inclined extremity 30A of the teeth 30 of the mobile element 22 generates on the latter a transversal component no longer affected by the guides 21A and 21B; such transversal component causes a rotary motion of the mobile element 22, with an angular movement of 15°: such rotary movement brings the inclined planes 30A of the two teeth 30 opposite to rest on the inclined planes 28 of the two guides 21A and 21B. Upon termination of the electrical supply, the heater 6 and the thermoactuator 5 cool down, with the consequent reduction of the pressure inside the sealed chamber and the interruption of the thrust on the piston 10; the force of reaction of the spring 12 therefore determines a return of the rod 11 in the withdrawal position, that in turn ceases the thrust on the sliding cursor 20. As a consequence the thrust on the mobile element 22 is also ceased, and thus on the rod 24. At this point the reaction of the spring 23, that operates on the rod 24, determines a contrary thrust on the mobile element 22; the inclined extremity of the teeth 30 push therefore on the inclined planes 28 of the guides 21. Such pressure causes the sliding of the inclined extremity of the teeth 30 on the inclined plane 28 (that therefore functions as a slide), i.e. a second rotary movement of the mobile element 22, with its one further angular movement of approximately 30°, until it arrives to the point visible in figure 2. In the condition illustrated in figure 2 (also in figure 1), therefore, the device is no longer electrically supplied, but the working position reached by the rod 24 is maintained. The commutation, i.e. the change of the balancing state of figure 2, is obtained with a successive electrical supply of the device. Such new supply determines, in a way similar to that already described, a new thrust of the sliding cursor 20, that freely slides along the guides 21 until it contacts the inclined planes 26 on the inclined extremities 30A of the two teeth 30; in particular such two teeth 30 are those which for the moment are not employed on the extremities of the guides 21A and 21B. The relative thrust permits the extremities 30A of the other two teeth 30 to free themselves from the inclined planes 28 of the guides 21A and 21B, that generates a new traversal component capable of causing a rotary motion of the mobile element 22: in this way an angular movement of approximately 15° is obtained that permits the inclined extremities 30A of the teeth 30 to reach in support the inclined planes 29 (fig. 2) of the guides 21A and 21B. With the successive termination of the electrical supply to the actuator 5, as described above, the return is determined of the withdrawal position of the rod 11 that ceases the thrust on the sliding cursor 20, and thus on the mobile element 22; as a consequence the reaction of the spring 23, that operates on the rod 24, determines once again a contrary thrust on the mobile element 22; the thrust of the inclined extremity 30A of the teeth 30 on the inclined planes 29 causes a rotary motion of the mobile element 22, with a further movement of 30° In such situation the teeth 30 return therefore to the initial position, i.e. of restraining the linear sliding by way of the guides 21A and 21B, in such a way that, under the thrust of the spring 23, the withdrawal of the rod 24 is permitted. We are therefore returned to the position illustrated in figure 5. It is to be noted that the particular configuration described, with an adapter CB equipped with the said system of inclined planes and/or cams, allows for obtaining a bistable system of greatly reduced dimensions; moreover, in the case described, the power characteristics of the thermoactuator 5 allow for managing high charges; as a consequence of which the monostable actuator DA can therefore easily be transformed to a bistable actuator, in a simple and modular manner by way of said adapter, inasmuch the components illustrated DA and CB can be assembled and tested separately. In the figure 6 the bistable actuator device subject of the present invention is represented in an embodiment being particularly advantageous, i.e. in an application of a door blocking for electrical household appliances, such as washing machines and/or cooking ovens; such safety system is shown to be particularly useful in the case of washing machines for avoiding opening of the door during use, and in the case of cooking ovens for avoiding opening of the door for example during pyrolysis cleaning procedures. In figure 6 with 40 said door blocking device as a whole is indicated, which has a body 41, a door blocking element 42 and a micro-switch 43, for the detection of the various functional conditions. As is seen, the device 1 according to the invention is integral with a housing body 41 and its rod 24 operates, in the above described manner, thrusts and maintains in position, on the blocking element 42, which is hinged in point 44 and restrained in point 45; the micro-switch 43, by way of its lever 46, detects the two working positions of the element 42. From the given description the characteristics of the device subject of the invention are clear, as are clear its advantages. In particular, in the described embodiment: the use of a thermoactuator 5 allows for developing considerable power with the aim of moving even heavy loads, for example in the order of 20 kg, even though being of greatly reduced dimensions: the body 2-3 of the illustrated device 1 has in particular the following dimensions: mm 17 x 18,5 x 71,5 (flange 13 and 14, terminals 7 and rod 24 excluded); the use of an electric heater 6 of the PTC type allows to thermo-adjust the actuator 5 without the addition of other control systems, and therefore to obtain a precise control of the actuation device at a low cost; the use of a thermoelectric actuator, comprising a thermoactuator 5 and a PTC electric heater 6, allows to actuate with power the system independently from the voltage supply, while maintaining a low level of energy consumption; the bistable kinematic motion (CB) allows for a further saving in energy, during the long actuation cycles of the device 1, inasmuch it operates in working and/or rest conditions with short supply cycles; the particular inclined planes and/or cam structure of the kinematic system allows for obtaining a simple bistable mechanical system, of reduced dimensions and being highly reliable, able to maintain the thrust on great loads, also in the case of sporadic increases of the forces exercised on the rod 24; the relatively slow insertion times, normally of several seconds, allow for eliminating vibrations or noise during the supply cycle; the modularity of the system allows production and separate testing of the actuator and bistable parts, with a reduction of costs due to production wastage. From the above, it therefore results that the device according to the invention finds a field of application being far more greater than the devices of the type known, in that it functions correctly in the most varied conditions of use, in reduced spaces, without sophisticated control systems, with great loads and however with both high and low voltage supplies. It is clear that numerous variants are possible by the man of the art to the device described as an example, without for this departing from the novelty principles inherent in the inventive idea. Furthermore it is clear that the bistable actuation device illustrated and described in an application of a door blocking system for electrical household goods could advantageously be utilised for various uses, such as for example the opening/closing of air circulating flaps in no-frost refrigerators, or together with valves; in such second case, the device according to the invention allows for avoiding, due to its relatively slow insertion times, phenomena of turbulence normally known with the name "water hammering".

Claims: Actuator device capable of varying its operating conditions from a stable state of rest and a stable working state, comprising an actuator element (DA) having a monostable actuator (5) able to induce an axial outward movement of a first linearly movable rod (10,11) when said actuator (5) is activated and allowing an axial inward movement of said first rod (10,11) when said actuator (5) is deactivated, and an adapter (CB), for converting the linear movement of said first rod (10,11) into a bistable actuation, in order to maintaining said working state even when said actuator (5) is deactivated, said adapter (CB) comprising a second rod (24), an elastic element (23) acting upon said second rod (24) and biasing said second rod (24) towards said first rod (10,11), said second rod (24) being capable of a movement opposing the force of said elastic element (23), a body (3) receiving at least a part of said second rod (24) and said elastic element (23) and formed internally with guide means (21A,21B), characterized in that a first element (20) is provided, being axially slidable with respect to said body (3) between said first rod (10,11) and said second rod (24), and prevented from rotation by said guide means (21A,21B); a second element (22) is provided, being juxtaposed with said first element (20) and slidable and rotatable with respect to said body (3) between said first rod (10,11) and said second rod (24); wherein said first and second elements (20,22) have inclined surfaces (26,30A) mutually engageable, for rotating said second element (22), upon engagement of said first element (20) with said second element (22) under a thrust applied by said first rod (10,11), and said second element (22) has protrusions (30) engageable with ends (28,29) of said guide means (21A,21B) for retaining said second element (22) and said second rod (24) in said working state after a first displacement of said elements (20,22) by said first rod (10,11), whereby a successive displacement of said elements (20,22) by said first rod (10,11) enables said protrusions (30) to become disengaged from said ends (28,29) of said guide means (21A,21B) and said elastic element (23) to retract said second rod (24). Device, according to claim 1, characterized in that said protrusions comprises radial teeth (30) of said second element (22). Device, according to claim 1 or 2, characterized in that said protrusions or teeth (30) and said ends (28,29) of said guide means (21A,21B) comprises inclined surfaces. Actuator device, according to claim 1, characterized in that said actuator element (DA) comprises a thermal actuator (5) having an actuator body (8) being thermally and/or electrically connected to an electric heater (6), in said body (8) being defined a chamber filled with a thermally expandable material (9), in particular wax, a piston (10) being at least partially inserted in said chamber, the expansion of said material (9), when made subject to a temperature increase induced by said heater (6), being capable of determining a thrust on said piston (10) towards the outside of said actuator body (8). Device, according to claim 1, characterized in that said actuator element (DA) and said adapter (CB) have respective bodies (2,3), which can be mutually connected, in particular by way of mutual hooking means (13-16). The use of the device according to at least one of the previous claims, for blocking the door of an electrical appliance, in particular a washing machine or a cooking oven, The use of the device according to at least one of claims 1 to 5, for the opening and the closing of air circulation flaps in a no-frost refrigerator. The use of the device according to at least one of claims 1 to 5, in combination with valves.

Inventors: CERRUTI DANIELE, SASSONE LUIGI, CERRUTI, DANIELE, SASSONE, LUIGI
Applicants: ELTEK SPA, ELTEK S.P.A.
Application year: 1994
Main classification: G05D23
IPC codes: F03G7, G05D23